1. Field of the Invention
The present invention relates to an engine idling control device in which an air flow rate control valve is provided along a passage for bypassing a throttle valve and supplying auxiliary or secondary air into an intake pipe.
2. Description of the Related Art
In a normal idling condition of an automotive engine, a negative pressure (for example, xe2x88x9273 kPa (in the order of xe2x88x92550 mmHg)) is generated within an intake pipe of a throttle body when a throttle valve is in a fully closed state. To this end, there has been proposed an automotive engine in which a bypass intake passage is provided on a throttle body, for establishing a communication between an upstream and a downstream side of the throttle valve, whereby a required amount of intake air is supplied by a secondary air supply device such as an RACV or an EACV (an idle control valve) for controlling the opening of the bypass intake passage to thereby perform the idling control of the engine (for example, Japanese Patent No. 2859530).
In an idling condition, however, when the engine load is increased by putting in the operation of several lamps and an air conditioner, in order to cope with the engine load, the opening value of an RACV is increased, but the intake negative pressure decreases (for example, about 29 kPa (in the order of xe2x88x92220 mmHg)), and this causes a problem that a sufficient quantity of intake air cannot be obtained even with the same opening area.
In addition, the recent growing tendency toward energy conservation demands highly fuel economy vehicles, and as a result of such a demand, for example, a so-called hybrid vehicle has been provided in which an engine (an internal combustion engine) and an electric motor are used in combination. Among the hybrid vehicles, there is a vehicle using a small displacement, high compression ratio engine with a view to improving the fuel economy.
However, in the small displacement, high compression ratio engine, the engine torque tends to become insufficient due to the small displacement, and the knocking toughness is reduced due to the high compression ratio. Due to this, particularly at the time of parking while idling in a high temperature atmosphere, the ignition timing is retarded, whereby the intake gauge pressure becomes higher than the normal level, a high load being thereby applied to the engine. When this takes place, the difference in pressure between the upstream side and the downstream side of the secondary air supply device becomes small, and therefore this causes a problem that an expected quantity of secondary air cannot be obtained.
It is an object to realize an idling control device which can control an engine into a stable idling state against various factors increasing an engine load at the time of idling by solving the aforesaid problem, in particular, for a small displacement, high compression ratio engine.
According to the invention, there is provided an engine idling control device having a secondary air supply device provided along a bypass intake passage communicating with an intake pipe and bypassing a throttle valve, an intake gauge pressure detecting unit for detecting an intake gauge pressure on the intake pipe side, and a secondary air supply control unit for controlling the secondary air supply device so as to open and close the bypass intake passage when an engine is in an idling state, wherein the secondary air supply device is controlled so as to put in any state the opening value relative to the bypass passage, and wherein the secondary air supply control unit controls such that the secondary air supply device increases the opening value relative to the bypass intake passage as the intake gauge pressure becomes higher than the predetermined low load condition in an idling state.
According to the construction, in the idling state, since the opening value of the bypass intake passage is varied in response to the variation of intake gauge pressure, even if the intake gauge pressure exceeds the normal level due to the influence of a retarded ignition timing, for example, at the time of parking while idling in a high temperature atmosphere, a high load being thereby applied to an engine, separately from the increase in load resulting when lamps and an air conditioner are turn on, a variation of intake gauge pressure resulting therefrom can be detected to be obtained a quantity of secondary air which can deal with the increased load.
In addition, the increasing rate of the opening value by the secondary air supply device can be controlled such that it becomes smaller depending on the intake gauge pressure becoming higher, and according to the construction, a required quantity of secondary air can be supplied in a more precisely and preferably control.